The present invention relates to a method of improving the control behavior of an anti-lock control system, in particular, for improving the steerability of the automotive vehicle and the driving stability when driving around a curve, wherein a vehicle reference speed is derived from the rotating behavior of the vehicle wheels and criteria are obtained for identifying a cornering situation and the direction of a curve, and wherein, upon identification of a cornering situation, a special or curve control mode is initiated in lieu of the standard control mode, thereby causing already in the partial deceleration area a reduction of the brake pressure on the front wheel on the inner side of the curve and/or on the rear wheel on the inner side of the curve, and wherein filtered wheel slip values are formed and evaluated for identifying a cornering situation.
During identification of a cornering situation, in a control method of the afore-described type, a moment of yaw balancing and stabilizing the cornering situation is generated about the vertical axis of the automotive vehicle through the pressure relief on the wheels on the inner side of the curve. The brake pressure on the wheels on the outer side of the curve, upon commencement of the control during a partial deceleration, is kept constant or is automatically increased in that a further brake pressure build-up on the wheel(s) on the inner side of the curve is precluded.
DE 34 13 738 C2 already discloses an anti-lock control system (ABS) comprising a system for identifying a cornering situation equally based on wheel slip measurement. For identifying a cornering situation, the slip values on the wheels on one side of the automotive vehicle are summed up and compared to the summation of slip on the other side of the vehicle to generate a signal identifying a cornering situation as soon as the difference between the slip summations exceed a predetermined threshold value. Upon identification of a cornering situation, selective criteria, such as "select-low" or "select-high" according to which the course of pressure is controlled in the individual brake pressure control channels of the said brake system, and threshold values for causing the said selective criteria to take effect will be varied, thereby enabling the control to be adapted to the varying conditions when driving straight-forward and when driving about a curve.
DE 21 19 590 A1 teaches to generate a signal for identifying a cornering situation with the aid of a transverse acceleration meter, such as a mercury switch.
Moreover, it is already known in the art to extend the functions of an ABS system in that the system is employed for improving the driving stability and the deceleration stability, respectively, when driving about a curve. To that effect, during cornering and during a partial deceleration, i.e. a deceleration process in which the ABS response thresholds are not achieved, a stabilizing moment about the vertical axis of the automotive vehicle is caused by a pointed delay of the brake pressure build-up on the wheels on the inner side of the curve compared to the brake pressure on the wheels on the outer side of the curve ("Bremsanlage und Schlupf-Regelsystem der neuen 7er-Reihe von BMW" ("Brake system and slip control system of the new BMW series No. 7"), ATZ 97 (1995), pp. 8-15; and "Bremsanlage und Schlupf-Regelungssysteme der neuen Baureihe 5 von BMW" ("Brake system and slip control systems of the new BMW series No. 5"), ATZ 98 (1996), pp. 188-194). In the absence of a steering angle sensor, the information on the current steering angle is derived from the transverse acceleration which, in turn, is computed from the wheel sensor signals.
The calculation of the filtered wheel slip and the evaluation of this quantity for determining criteria referring to a cornering situation have been described in non-prior-published patent applications DE 195 22 634 A1 and DE 195 22 632 A1. For identifying a cornering situation, according to these literature references, the filtered wheel slip values are compared to one another and are evaluated. Switching over to a cornering control mode occurs, once the filtered wheel slip on both front wheels and the filtered wheel slip on a rear wheel are above a predetermined maximum slip value and the filtered wheel slip on the second rear wheel a the same time is below a predetermined minimum value.
It is the object of the present invention to provide a method intended to improve the control behavior of an ABS system in a cornering situation already prior to reaching the actual ABS-threshold values in that the cornering situation is reliably identified alone from the wheel rotating behavior and, through interference with the deceleration process, a stabilizing moment about the vertical axis of the automotive vehicle is generated in a deceleration process upon occurrence of a cornering situation.
It has been found that this problem can be solved by a method involving the step of detecting the slip condition of the individual wheels by determining a slip difference value, i.e. the difference between the momentary wheel slip and the filtered wheel slip, and a summation slip value formed by integration of the difference between the momentary wheel slip and a predetermined permissive slip value, further including the step of detecting, by evaluation of the slip difference value and the summation slip value, a wheel-condition value, in particular, a value representing the angular slip or the transverse dynamics of the wheel which can, therefore, be evaluated for identifying a cornering situation, and further including the step of determining the condition of the vehicle by comparing the values of the angular slip of the individual wheels of the automotive vehicle.